An "optimistic message" is what Republican Sen.-elect Cory Gardner said helped him beat incumbent Democrat Sen. Mark Udall in Colorado on Tuesday — a message he suggests GOP candidates use nationwide.

"We really talked about an optimistic message. We talked about lifting people's eyes up to the Rocky Mountain horizon, that this is an ever-young state where we talk about an ever-hopeful attitude.

"That's the message we presented. And, that's the kind of thing that Republicans around the country need to do. Put together a positive agenda that is about moving forward, instead of just being about opposition," Gardner told "Fox & Friends" on Thursday.

Gardner said his campaign also assembled "an incredible ground game" that was unlike any other Republican effort in Colorado or the country. He suggested it was important for the Republican party to admit when it was broken, and then pledge to fix its problems — such as its positions on energy and immigration reform.

"If it's energy, we have to talk more about traditional energy, yes. Keystone pipeline, yes. But, also talk about renewable energy," he said. "We can't simply be against immigration reform. We've got to figure out a way to be for immigration reform that is something the Republican party can support — the House, the Senate, and the president."

Gardner said President Barack Obama would have a choice to either work with Congress on issues facing the country, or "show the American people that he and his party are refusing to work with us."

"Either the president becomes the key of obstruction, or the president is seen as somebody who can work with a Republican party that is mature and competent in its governance," he said.